Method and device for operating a hydraulic tool

ABSTRACT

An independent, portable hydraulic unit (80) for powering a hydraulic tool (C), and a method for operating the tool (c) with the aid of the unit. The unit includes a hydraulic circuit (1) having a pump (19) and a power source (17) and a pump motor (18). The pump (19) is intended to pressurize the tool (C) to a first pressure level (P2). The hydraulic circuit charges the hydraulic accumulator (22) to a maximum second pressure level (P1) which is at most equal to the first pressure level (P2). A check valve (31) isolates the hydraulic accumulator (22) from the pump pressure when this pressure exceeds the second pressure level (P1). A closure valve (12) and check valve (21) are provided for enabling the charged accumulator (22) to be connected to the tool upon activation of the unit so as to power the tool. A microprocessor (70) causes the pump (19) to charge the accumulator to the second pressure level while the tool is relieved of pressure, after emptying the accumulator (22). The power unit (80) is controlled so as to isolate the accumulator (22) from the pump after charging the accumulator to the second pressure level (P1). After emptying the accumulator into the took, the pump (19) pressurizes the tool (C) to the first pressure level (P2). The accumulator (22) is charged by the pump (19), while the tool (C) is relieved of pressure and isolated from the pump (19).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and to an hydraulic power unitof the kind defined in the respective preambles of the followingindependent method and apparatus claims.

The invention is concerned more particularly with a portable and"independent" type of hydraulic power unit intended to power a hydraulictool which is connected to the power unit by means of a hose and handledand manipulated by an operator. The hydraulic tool may have the form ofa crimping tool, crimping tongs, for instance.

2. Description of the Related Art

An arrangement of this kind is known from DE-A1-3835696.

Crimping tongs are tools by means of which an electrical end-contact canbe pressed onto the end of an electric cable or the like. In industrialapplications, such crimping tools may conveniently be hydraulicallyoperated, using an hydraulic piston-cylinder device as the power means.The cylinder is conveniently connected hydraulically to an hydraulicpower unit by means of a hydraulic hose, this power unit preferablybeing portable and also "independent", for many good reasons. By"independent" is meant that the unit will contain its own power source,for instance a rechargeable electric storage battery. The hydraulicpower unit will also include an hydraulic circuit having an hydraulicpump which is driven by a motor that can be connected to the powersource.

In the case of portable units it is necessary to take into account allsignificant points of view with regard to the operating functions of theunit. For instance, it is necessary for the pump to generate arelatively high pressure, for instance a pressure of 250 bars or more inorder for the working cylinder to produce a required force of 15 kN forinstance with the aid of an hydraulic cylinder of reasonablecross-sectional area, this cylinder also preferably forming the toolcore or handle.

On the other hand, the pump must be relatively small and relativelylight in weight in order for the hydraulic unit to be easily carried byhand, although this will result in a relatively long working cycle.

It is known, for instance, from U.S. Pat. No. 2,392,471, U.S. Pat. No.2,641,106, U.S. Pat. No. 3,375,658, U.S. Pat. No. 4,096,727 to includein an hydraulic circuit an hydraulic accumulator which is charged by thepump and which provides a relatively large volume flow capable ofquickly filling a working cylinder to a working state, as theaccumulator is emptied. However, the accumulator pressure fallsdrastically, therewith resulting in a low accumulator pressure when theworking cylinder is in its working state. Furthermore, from the aspectof weight among other things, it is unsuitable to give the accumulator avolume and pressure-durability which will enable the working cylinder tobe pressurized from the accumulator at a desired pressure (for instance250 bars).

It is actually unsuitable to construct the accumulator such as topressurize the working cylinder with the desired tool working pressureas the accumulator is emptied.

Accordingly, one object oft he invention is to provide a power unitwhich can include an hydraulic accumulator of relatively low pressureand of relatively small volume, while, at the same time, giving the pumpa relatively low flow capacity and low motor power, despite a high pumppressure and a high working pressure of the hydraulic cylinder of thetool. Another object of the invention is to provide a method ofoperation for one such unit.

These objects are achieved with a power unit having the characteristicfeatures set forth in the independent apparatus claim below, while theinventive method is characterized by the steps set forth in theindependent method claim.

Further embodiments of the invention are set forth in the dependentclaims.

Fundamentally, the invention requires the hydraulic circuit to includean accumulator which is dimensioned for a pressure which is at mostequal to and preferably slightly lower than the maximum pump-workingpressure, and which may advantageously be dimensioned for a much lowerpressure than the maximum pump-working pressure. When activated, theaccumulator fills the tool relatively quickly, so as to bring the toolto a state in which it engages the workpiece. Naturally, the accumulatorpressure will fall rapidly as the accumulator is emptied, but theprimary aim is to drive the tool quickly to its active state orposition, ie into engagement with the workpiece. The accumulator isemptied through a check valve and the hydraulic pump can be activated inconjunction with emptying the hydraulic accumulator or immediately afterhaving emptied the accumulator, wherein the pump pressure is isolatedfrom the accumulator and acts solely on the tool. Since the tool isgenerally filled with hydraulic fluid and engages the workpiece, thepump need only work to increase the pressure and no to fill thehydraulic cylinder so as to move the moveable part of the tool intocontact with the workpiece.

As soon as the pump has applied its maximum working pressure, orestablished a predetermined high level of pressure against the tool, thetool is isolated from the pump and the pump is caused to fill theaccumulator with hydraulic fluid while the tool is emptied of hydraulicfluid and opened to enable another workpiece to be placed in the tool.

Although the maximum pressure level of the accumulator may be equal tothe maximum pressure level of the pump, the accumulator maximum pressuremay be a slightly lower pressure, preferably a considerably lowerpressure level, with the intention of reducing the cost of theaccumulator as such.

The accumulator may be protected against overpressure with the aid of apressure relief valve fitted to the reservoir tank.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplifying embodiment of the invention will now be described withreference to the accompanying drawing, the single figure of whichillustrates generally an hydraulic circuit for an inventive power unit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in the drawing, the circuit includes a reservoir R and a line 1which leads from the reservoir R to a hose 5, which is connected, inturn, to a tool C. In the illustrated case, the tool C includes a handle60 which is formed by a working cylinder 61 having a piston 62 and apiston rod 63. The piston 62 is acted upon, or biassed by a returnspring 66 in a direction in which the hydraulic chamber defined betweenthe piston 62 and the cylinder 61 is emptied. A counter pressure surfaceor anvil 65 is connected to the handle or cylinder 60, wherein aworkpiece can be crimped between the anvil 65 and the piston rod 63 or acrimping jaw 64 fitted thereto.

An electric motor 18 is connected operationally to a hydraulic pump 19in the line 1. Check valves 10 and 11 are mounted in the line 1 onrespective sides of the pump 19. An hydraulic accumulator 22 isconnected to the line 1 downstream of the pump 19, through the medium oftwo parallel lines 2, 3. One line, 2, includes a check valve 21 whichfunctions to prevent flow in a direction from the line 1 to theaccumulator 22, and the other line, 3, includes a check valve 31 whichblocks the flow from the accumulator 22 to the line 1. However, thecheck valve 31 is not controlled solely by the pressure differencebetween the line 1 and the accumulator 22, but is also controlled by apilot pressure from the line 1 downstream of the closure valve 12. Thecircuit also includes a pressure sensor 14 which senses the pressure inthe line 1. A pilot pressure originates from the line 1 at its outletend and is led to the check valve 31 through a pilot line 90, in orderto keep the valve 31 closed when the pressure sensed by the pressuresensor 14 is equal to the pressure in the line 1 on the output side ofthe pump 19, despite the accumulator 22 holding a lower pressure thanthe line 1.

As will be seen from the drawing, the illustrated circuit also includesa return line 4 which is connected to the line 1 downstream of theclosure valve 12 and which opens into the reservoir R. The line 4includes a valve 15 in the form of a solenoid valve, which is normallyopen. Also included is a pressure limiting valve 16 which is connectedto the line 1 on the pressure side of the pump 19 and through whichhydraulic fluid is drained to the reservoir R when the pressure in theline 1 exceeds a given limit value. A pressure sensor 13 is connected tothe line 1 between the pump 19 and the closure valve 12.

An electric storage battery 17 is connected to the motor 18 via a switch40. The switch 40 is controlled by a microprocessor 70.

The tool C includes an operating switch CB which is connected to themicroprocessor 70 by a signal cable 50. The tool C also includes anacoustic signal emitter CS and a light signal emitter CL. Themicroprocessor senses and monitors the pressure level of the hydraulicaccumulator circuit through a pressure sensor 13 which functions toindicate that charging of the hydraulic accumulator 22 is complete andthat the accumulator has obtained a given pressure, when sensing apredetermined pressure level. The microprocessor also senses thepressure at the output of line 1, the switched state of the valve 15,and the switched state of the valve 12. The microprocessor 70 alsofunctions to monitor the battery supply voltage of the electricalbattery 17 and the temperature of the hydraulic circuit.

Some of the components shown in the drawing have been identified withdouble reference signs. For instance, the normally closed solenoid valvehas been referenced 12 and also V1. Furthermore, the normally opensolenoid valve 15 has been referenced 15 and V2. The pressure sensorwhich produces an output signal when charging of the hydraulicaccumulator 22 is complete has been referenced 13 and P1. The pressuresensor 14 which produces an output signal upon completion of a toolworking cycle has been referenced 14 and P2. The check valve in the line2 has been referenced 21 and CV. The pilot-controlled check valve in theline 3 has been referenced 31 and POCV. The pressure limiting valve hasbeen referenced 16 and RV. The microprocessor has been reference 70 andMC. The rechargeable electric storage battery has been referenced 70 andEA, while the pressure accumulator has been referenced 22 and HA.

The portable, independent power system illustrated in the drawingincludes generally the tool (C) which is connected freely moveable bythe hydraulic hose 5 to an hydraulic power unit which includes thehydraulic circuit illustrated within the square defined by the chainline 80. The hydraulic power unit is controlled by control electronicsincluded in the microprocessor 70.

The illustrated system works as follows:

A main switch (not shown) is switched on and a green lamp (not shown)lights up on the base unit 80. The electronic 70 check the status of theunit 80 with regard to battery voltage and also checks the state of thehydraulic accumulator 22. If the battery voltage 17 is too low, awarning lamp on the base unit lights up and a corresponding warning lampincluded in the light signal unit CL on the tool C will also light up.If the pressure prevailing in the hydraulic accumulator circuit does notcorrespond to the setting on P1, the motor 18 and the pump 19 are setinto operation, wherein charging of the accumulator 22 is terminated(the motor 18 and the pump 19 are stopped) when the pressurecorresponding to the setting on P1 has ben reached.

A further indicating lamp, for instance a green indicating lamp,included in the arrangement CL on the tool handle may now be switched onand a corresponding acoustic signal may be produced to indicate to theoperator that the unit 80 is now ready for use.

The electronics 70 are maintained activated over a period of 10 minutes,to allow the operator to activate an operating button CB on the tool C.If nothing happens within this waiting period, all indicators areextinguished and the arrangement adopts a so-called "sleep mode", inorder to save battery energy. The base unit 80 can be restarted byswitching the main switch on and off, or by pressing a restart button onthe operating handle.

The working cycle is started, by activating the operating button CB. V2is closed, whereafter V1 is opened. The hydraulic accumulator 22 isemptied into the tool C through the check valve CV. In order toestablish the pressure preset at P2, the motor 18 and the pump 19 arestarted-up when the pressure rises in the control line X/90. Theaccumulator circuit is blocked by CV and POCV. When the pressure at theoutlet of the line 1 corresponds to the setting on the sensor P2, thevalve V1 closes and the valve V2 opens so as to evacuate the hydraulicfluid in C to the reservoir tank R. This evacuation of the hydraulicfluid is supported by the tool return springs 66. The working cycle isnow terminated.

When the pressure in the accumulator circuit does not correspond to thesetting on the pressure sensor P1, the motor 18 and the pump 19 areagain started-up. Charging of the accumulator 22 is terminated (themotor 18 and the pump 19 are stopped) when the pressure againcorresponds to the pressure setting on the pressure sensor P1. Theacoustic and light indicators can now be activated, to indicate that thearrangement is ready for the next working cycle.

The battery voltage, the pressure level of the accumulator circuit andthe temperature of the hydraulic circuit are monitored continuously. Thearrangement is controlled by a microprocessor through an 8-bit RISCmicrocontroller. The safety valve or pressure relief valve RV servesonly to protect the hydraulic circuit against overpressure.

V1 and V2 are seat valves which provide a good sealing effect. It willbe obvious to the person skilled in this art that the valves V1, V2 canbe replaced with a 3/2-way valve.

The hydraulic accumulator 22 may be made safe with the aid of a pressurerelief valve corresponding to the valve RV/16 which normally dischargesto the reservoir tank and which prevents pressurization of theaccumulator above its upper pressure limit when this pressure limit islower than the maximum pump pressure.

One advantage afforded by the invention is that there can be used asmall, simple pump which is designed for a relatively high pressure anda relatively small hydraulic flow while still being able to establishrapid primary filling of the tool working cylinder with the aid of anaccumulator which need only be designed with respect to the volumerequirement of the tool and which in the final stage of an emptyingprocess need only provide a relatively low pressure in the tool, thispressure being sufficient to drive the tool to its closed position,whereafter the tool working pressure is established finally by the pumpover a short period of time owing to the tool being filled from theaccumulator. A further advantage is obtained because the hydrauliccircuit is constructed to enable the accumulator to be charged withhydraulic fluid while the hydraulic fluid in the tool is drained intothe reservoir tank (the tool is opened). Still another advantage isafforded by the fact that the accumulator can be chosen for a maximumpressure level which is lower than the pump working pressure, i.e. lowerthan the maximum pump pressure.

Still another advantage is afforded by the fact that the hydraulicaccumulator is emptied into the tool through a first check valve and ischarged or replenished from the pump through a controllable second checkvalve which is guided to a closed state under the (direct) influence ofan hydraulic pressure (pilot pressure) applied through the tool supplyhose.

We claim:
 1. A method for operating an hydraulic tool (C) having anindependent, portable hydraulic power unit (80) which includes anhydraulic circuit (1) having a pump (19), a power source (17), apump-operating motor (18) operable from the power source, and a motorcontrol means (40), wherein the pump (19) is adapted to produce apredetermined first pressure level (P2) for corresponding pressurizationof the tool (C), characterized by charging an hydraulic accumulator (22)connected to the hydraulic circuit (1) to a second hydraulic pressurelevel (P1) which at most is equal to the first pressure level (P2) thatcan be produced by the pump (19); emptying the charged accumulator (22)into the tool for initial activation thereof, wherein the accumulator isadapted to maintain when empty a pressure level which is considerablylower then the first pressure level; causing the pump (18) to actagainst the tool filled from the accumulator (22) after emptying of theaccumulator, while isolating the accumulator from the pump so as toestablish a tool working pressure which corresponds to the firstpressure level P2, and thereafter isolating the tool (C) from the pump(19) and emptying the hydraulic fluid content of the tool into the tank(R); and by causing the pump (19), isolated from the tool (C), to chargethe accumulator (22) to the second pressure level.
 2. A portableindependent hydraulic unit (80) for operating an hydraulic tool (C)which can be connected to the unit (80) by means of a hose (5), whereinthe unit includes an hydraulic circuit (1) which includes a pump (19), apower source (17) and a pump-operating motor (18) that can be driven bythe power source, and a motor-control device (70), and wherein the pump(19) is constructed to produce a predetermined first pressure level (P2)which can be transmitted to the tool (C), characterized in that thehydraulic circuit (1) includes means (31, P2, X) for charging thehydraulic accumulator (22) to a maximum second pressure level (P1) whichis at most equal to the first pressure level (P2); in that the means(31, P2, x) include means (31) for isolating the hydraulic accumulator(22) from the pump pressure when said pump pressure exceeds apredetermined maximum pressure level (P1) of the hydraulic accumulator;and in that when activating the unit to pressurize the tool firstregulating means (V1, 21) function to first allow the chargedaccumulator (22) to be connected to the tool (C) for primary activationof the tool; and in that second regulating means (12, 14, 90) functionto cause the pump (19) to charge the accumulator (22) to the secondpressure level while the tool is isolated from the pump.
 3. A unitaccording to claim 2, characterized in that the isolating means (31) iscontrolled by the output pressure of the hydraulic circuit (1).
 4. Aunit according to claim 2, characterized by means (CB, V1, 2, 21) foremptying the accumulator (22) into the tool (C), means (MC, P2) foractivating the pump subsequent to emptying the accumulator, so as toincrease the hydraulic pressure in the tool (C) to said predeterminedfirst pressure level (P2), means (66, V2) for emptying hydraulic mediumfrom the tool (C) into the tank (R), means (MC, P1, V1) for charging theaccumulator (22) to the second pressure level (P1) by operating the pumpwhile the tool (C) is relieved of hydraulic pressure and isolated fromthe pump (19), and means (P2, X, 31, 3, 2, 21) for isolating theaccumulator (22) from the pump (19) when the pump works towards the tool(C).
 5. A unit according to claim 2, characterized in that the circuit(1) includes an hydraulic line (1) which extends from the pump to thetool and which includes a closure valve (V1); in that a pressure sensor(P2) is connected to the line (1) between the closure valve (V1) and thetool (C); in that a return line (4) which includes a closure valve (15)and which leads to the tank (R) is connected to the line (1) at alocation between the closure valve (12) and the tool (C); in that thehydraulic accumulator (22) is connected by two parallel line (2, 39) tothe line (1) between the pump (19) and the closure valve (12); in thatone accumulator line (2) includes a first check valve (21) which opensto flow in a direction towards the line (1), and the other accumulatorline (3) includes a second check valve (31) which opens to flow in adirection away from the line (1) and towards the accumulator (22); inthat the second check valve (31) is adapted to be moved towards a closedposition by the pressure in the line (1) between the closure valve (12)and the tool (C) so as to maintain the accumulator (22) isolated fromthe pump when the pump pressure exceeds the second pressure level; andin that a second pressure sensor (P1) is connected to the line (1)between the closure valve (V1) and the pump (19) so as to enablecharging of the accumulator (22) to be interrupted when the secondpressure sensor senses the second pressure level (P1), while the pump(19) is maintained isolated from the tool (C) by the closure valve (V1).